You should have your Sansa player set to MTP (Media Transfer Protocol) when you are using it with any of the supported subscription (ie) iTunes, or Rhapsody music services. The main purpose of MTP is to transfer media files and associated metadata to/from devices, with optional additional support for reading and setting of device parameters such as special DRM-related device parameters for restricted content. Otherwise, you should set it to MSC (Mass Storage Class), which is the normal USB mode for storage devices like thumb drives, and camara SD memory cards.
See this tip posted here Tips on MP3 connection problems..
MTP stands for Media Transfer Protocol. It is a Microsoft standard and is Microsoft's solution to connecting MP3 players and cameras to a w*ndow based Computer. MTP mode must be used in order to transfer ANY Digital Rights Management (DRM) protected content. MP3's downloaded form services like Rhapsody and Napster will only function in this MTP mode.
Things to do if you are getting not enough space mesage.
1. Turn device OFF.
2. Facing the hold switch slide it to the right so an orange color would show putting the device on Hold.
3. Connect the device to the PC.
If you added songs to the device in MSC mode, then you switched to MTP mode, you will not be able to see the songs added in MSC mode and vice versa, though the space used on the player will still reflect their presence. Switching modes should make the files show up. For example, switching back to MSC or MTP mode.
For older players - e200v1, c200v1, c100, m200 - the files become hidden files if the modes are switched. An easy workaround is to edit the folder options to show hidden files.
STEP 1 - Edit the folder options of the computer to show the hidden files
1. Double-click My Computer.
2. Under the Tools menu, select Folder options, then click the View tab.
3. Under Hidden files and folders option, select Show hidden files and folders.
4. Uncheck the Hide protected operating system files (Recommended) check box.
5. Click Apply, then click OK.
1. Double-click Computer.
2. Click the Organize button on the upper left corner.
3. Click Folder and search options.
4. Click the View tab and select Show hidden files and folders.
5. Uncheck the Hide protected operating system files check box.
6. Click Apply, then click OK.
SOLUTION 2 - Perform a Check Disk.
STEP 1 - Switch to MSC mode
1. On your Sansa player, switch the USB mode to MSC.
2. Connect the Sansa player to the PC.
STEP 2 - Perform Check Disk
1. Locate the Sansa player under My Computer.
2. Right-click the removable drive associated with the Sansa player, and select Properties.
3. Click the Tools tab, and then click Check now.
4. Click to select the Automatically fix the file system errors and Scan for and attempt recovery of bad sectors check boxes.
5. Click Start.
SOLUTION 3 - Format the player in MSC mode or MTP mode.